<!--输出结果为1,2,undefined,3-->
<!--0<100<0在进行比较时会类型转换-->
<!--a中会有变量提升，所以是undefined-->
<!DOCTYPE html>
<head> 
<meta charset="utf-8"> 
 <title>菜鸟教程(runoob.com)</title> 
</head>
<body>
    <div style="height:1px;overflow:hidden;background:red"></div>
    <script>
        var x = 1; 
        function a() { 
            console.log(x); 
            var x = 2; 
            x++; 
            console.log(x); 
        }
        function b() {
            console.log(x); 
            x++; 
            console.log(x);
        } 
        if(0 < 100 < 0) {
            a();
        } else {
            b();
        } if(0 < 100 < (0 + 4)) {
            a();
        } else {
            b();
        }
    </script>
</body>
</html>